Combustion supervision system



Aug. 18, 1970 P. J. CADE coMBUsTIoN sUPERvIsoN SYSTEM Filed June 17,1968 m @E asv Pr @N N -N H slllow @m m95@ mma hl i\/N.N u!

Nm om o. @Q vm w q, wm K v x. .h n n/f Hwom. Q -m Nm. M mqwmqq -QAM .IMDU- \NN w- 22: zoEzQ EJE mas q mma/2m ON -om @Nw/1 m -m F. Q @om Q wwwv o@ Niv 3% QE EMM i w United States Patent O 3 524,717 COMBUSTIONSUPERVISION SYSTEM Phillip J. Cade, Winchester, Mass., assignor toElectronics Corporation of America, Cambridge, Mass., a corporation ofMassachusetts Filed `lune 17, 1968, Ser. No. 737,491 Int. Cl. F23n 5/ 00U.S. Cl. 431-29 18 Claims ABSTRACT OF THE DISCLOSURE A combustioncontrol system includes four similar adjustable electronic timers, eachincluding a unijunction transistor, a capacitor, and a variableresistor, and each controlling a relay coil. A first timer times a purgeinterval, and at the end of the purge interval initiates operation oftwo other timers, a first of these two timers timing an ignitioninterval and the second of these two timers delaying application of themain fuel supply to the combustion chamber. The fourth timer times aninterval at the end of the ignition interval and then releases the relaycontrolled by the rst timer.

SUMMARY OF INVENTION This invention relates to electrical timing andcontrol circuitry and more particularly to timing and control circuitryparticularly adapted for use in combination supervision systems.

In connection with the safe operation of combustion systems, it isdesirable to sequence the fuel burner equipment automatically through aseries of steps to initiate the desired combustion condition in thesystem and then to supervise on a continuing basis that establishedcombustion condition in a manner to promptly shut the combustion systemdown in safe condition upon occurrence of flame or equipment failure.The desired operations to be performed in sequence in start up of acombustion system and the timing of those operations may differextensively depending on the application and code specifications, forexample. It is desirable that the timing of the sequence of operationsbe accurate and versatile and that the control be capable of providing ashort time interval where desired. Accordingly it is an object of thisinvention to provide a simple, versatile and reliable electrical timingand control circuit for use in a combustion control system.

Another object of this invention is to provide novel and improved flamerelay control apparatus for use in a combustion supervision system.

Another object of the invention is to provide a novel and improvedarrangement for checking in a coordinated and reliable manner the properoperation of a flame supervision system.

Another object of the invention is to provide a novel and improvedtiming and control circuit particularly adapted for supervising acombustion system that does not employ motor driven timing devices.

Still another object of the invention is to provide a novel and improvedcontrol arrangement for use in a combustion control system that employsa plurality of electronic timers.

In accordance with the invention, there is provided timing and controlcircuitry for use in a combustion control system that includes a fuelcontrol element; an ignition control element; a flame detector; andcircuitry responsive to an operating request signal and to the llamedetector for controlling the operation of the ignition and fuel controlelements to provide in sequence an ignition interval, and a combustioninterval. This timing and conice trol circuitry includes a plurality ofadjustable electronic timers which time an ignition interval in whichllame is established in the combustion chamber and initiate theapplication of the main fuel source after detection of establishment offlame in the combustion chamber. The timing cycles of the timers overlapso that the two timers are operating concurrently and provide a check onthe proper operation of the control circuitry. In one embodiment, onetimer initiates the flow of main fuel after a second timer hasterminated the ignition condition. In a preferred embodiment, threetimers are employed during the ignition interval, two timers commencingtiming cycles simultaneously at the beginning of the ignition interval,thevtimer first ending its timing interval enabling a flame indicatorand also starting a third timer; the second timer initiating the flow ofmain fuel at the end of its timing interval if the flame has beenestablished; and the third timer then terminating operation of theignition components of the combustion system. The circuitry shuts downthe system in safe condition whenever an unsafe condition is detected,for example, detection of a flame indication prior to initiation ofignition, failure to detect llame Within the a predetermined period, orfailure of flame after it is established. In a preferred embodiment ofthe invention, a fourth timer is employed which provides an initialpurge interval and then initiates the ignition and fuel flow sequences.The circuitry is arranged to provide economical use of circuitcomponents in a reliable manner.

In a preferred embodiment of the invention, each electronic timer is ofsimilar design and includes a capacitive element. An active switchelement (a unijunction transistor in a particular embodiment) isemployed in conjunction with a load device such as a relay coil toprovide an indication of the termination of the timing interval, therelay coil being held in by a holding contact.

A further feature of the invention is the employment of the llame relaycoil as a component of an electronic timer in a manner in which theflame relay performs a checking function prior to initiation of theignition interval, it being used as a component of a timer during theignition interval, and then its function is returned to flamesupervision. In a particular embodiment at the completion of the timinginterval, the electronic timer initially energizes the flame relay coilindependently of the presence of flame in the supervised combustionsystem and initiates a timing interval which is employed to terminateignition. The llame relay coil is held in, however, only if flame issensed in the supervised combustion chamber.

In the preferred embodiment of the invention, the control will shut downthe system` in safe condition should any one resistor open or anytransistor fail in short or open condition; as well as locking out insafe condition upon detection of any unwanted or defective condition inthe supervised system or in the control equipment. The inventionprovides a timing and control circuit employing electronic timers thatare operating simultaneously so that the failure of either one will bedetected safely. An accurate, versatile and safe timing control systemfor use in combination supervision systems is provided in which a shorttiming intervals may be provided where required by particularspecifications.

Other objects, features and advantages of the invention will be seen asthe following description of a particular embodiment thereof progresses,in conjunction with the drawings, in which:

FIG. l is a block diagram of components employed in the control of acombustion system in accordance with the invention;

FIG. 2 is a schematic diagram of sequencing circuitry for controllingthe sequence of operation of the elements shown in FIG. l; and

3 FIG. 3 is a timing diagram indicating the sequence of operationprovided by the circuitry of FIG. 2.

DESCRIPTION OF PARTICULAR EMBODIMENT With reference to FIG. 1, lineterminals and 12 are provided for connection to a suitable source ofelectric power. Connected in series across terminals 10, 12 is normallyclosed contacts 44-1 of a magnetic lockout switch actuator 44 (FIG. 2),the normally open contacts -1 of main control relay 20, and a blower 16.Connected to the junction between contacts 44-1 and 20'-1 is line 13which applies power to the primary winding 30 of control transformer 32(FIG. 2). An operating control (diagrammatically indicated as switch 14)which is closed upon a request for operation of the supervised burnersystem is connected between terminal 10 and other control components ofthe system. Normally open lockout contacts 44-2 and an alarm unit 18 areconnected in series between switch 14 and terminal 12. The coil 20 ofthe main control relay is connected across contacts 44-2 and alarm 18.Other control connected in parallel with relay coil 20 include a damper22, a pilot fuel control 24, ignition control 26 and main fuel control28.

These compounds are controlled by the electronic timing circuitry shownin FIG. 2. With reference to that iigure, the primary winding ofstepdown transformer 32 is connected across the terminals 10, 12 vialine 13 and contact `44-1. Transformer 32 has a secondary winding 34 towhich is connected a rectifier 36 and smoothing capacitor 38 so that arectied 24 volt signal is applied across lines 40 and 42. Connected toline 40 is normally open control relay contacts 20-2, in series with airflow responsive switch 16-1 and magnetic lockout actuator 44. A iiamesensor 62 applies a signal through llame detector electronics 64 to thecontrol electrode 66 of switch transistor 86 when ilame is detected inthe supervised combustion chamber.

The circuitry also includes four electronic timing circuits, each ofwhich includes a unijunction transistor and a timing network thatincludes a capacitor and a variable resistor. The first electronictiming circuit includes transistor 50, timing capacitor 52, variabletiming resistor 54, and a biasing resistor 56. A relay coil is connectedbetween the output electrode 62 of the unijunction transistor 50 and thetransistor switch 120. A second timing circuit includes unijunctiontransistor 70, timing capacitor 72 variable timing resistor 74 andbiasing resistor 76.

The output electrode 78 of the transistor 70 is connected to tap 80 ofthe coil 82 of the ame relay. A third timing circuit includes transistor90, timing capacitor 92, variable timing resistor 94 and biasingresistor 96. Relay coil 98 is connected to output electrode 100 of thetransistor 90. Resistor 102 provides a discharge path for capacitors 72and 92 when the control is in standby condition. A fourth timingcircuit, which includes unijunction transistor 110, timing capacitor 112and variable resistor 114, is connected to the control electrode 118 ofswitch transistor 120.

In each of these timing circuits, when a DC potential is applied to thecircuit, the signal applied to the output circuit of the transistorestablishes a bias potential on the emitter electrode of the transistor.The timing network of the variable resistor and the timing capacitor isalso energized and the capacitor commences to charge. When the potentialon the timing capacitor exceeds the bias potential on the emitterelectrode, the transistor conducts and the capacitor discharges throughthe transistor and the relay coil to cause energization (pickup) of therelay controlled by the timer (except in the case of the fourth timerwhich switches off transistor 120). With the energization of its coil,the relay closes one of its contacts to complete a holding circuit tomaintain it en ergized. Other contacts are operated by the energizedrelay to control the operation of one or more combustion controlelements and/or another timer.

The sequence of operations of the components shown in FIG. 1 ascontrolled by the circuit shown in FIG. 2 is indicated in FIG. 3. Aninitial prepurge interval which may be varied from zero to ninetyseconds is controlled by the rst timing network that includesunijunction transistor `50. At the end of that rst timing interval,relay 60 is energized and two other timing intervals are initiated, asecond timing interval (variable from two of fifteen seconds) controlledby circuity associated with transistor 70 and a third timing interval(variable from four to twenty seconds) controlled by the circuitryassociated with transistor 90. A fourth timing interval (variable fromfour to sixty seconds), under the control of the circuity associatedWith transistor 110, is initiated in respouse to the conjointtermination of the second timing interval and the detection of flame inthe combustion chamber and at the end of that timing interval, thesystem is transferred to full operation with the de-energization ofrelay 60.

In response to a request for system operation, operating control 14closes. The main control unit coil 20 is energized, closing contacts20-1 to energize blower 16 and closing contacts 20-2 in the input to thetiming circuitry. When air llow has been established in the combustionchamber, the air flow responsive switch 1641 closes and power issupplied through the lockout actuator coil 44. Should a llame signal beapplied to control electrode 66 at this time, transistor 86 will conductand energize llame relay 82, closing contacts 82-2 so that as soon asair ow is produced in response to a request for burner operation thelockout actuator 44 will open contacts 44-1, terminat ing the controlsequence; and close contacts 44-2, energizing alarm 18. If a flamesignal is not present, the first timing (prepurge) interval continues aspower is applied via the normally closed contacts 98-1 and the normallyclosed contacts 60-1 to apply a bias potential, via resistor 56, to theunijunction transistor 50. This DC signal also is applied via variableresistor 54 to charge capacitor 52. When the potential on capacitor 5.2exceeds the bias potential applied to the emitter of transistor 50, thetransistor conducts and capacitor S2 discharges through the transistorsoutput circuit to energize the relay coil 60 (the current path beingcompleted to ground through the transistor switch 120` which conducts inresponse to the signal applied via resistors 122, 124). With theenergization (pickup) of relay coil 60 its contacts are operated;contacts 60-1 open to interrupt a lockout actuator energizing circuitvia llame relay contacts 82-2; contacts 60-2 close to complete a holdingcircuit; contacts 60-3 close to commence timing operation of the secondand third timing circuits; normally closed contacts 60-4 open,de-energizing the damper control 22 (FIG. 1); contacts 605 close,energizing the pilot fuel control 24 and the ignition control 26 (thelatter through the normally closed contacts 82-3 of the ilame relay);contacts 61)6 open disabling the circuit to the flame sensor transistor86 so that the flame relay 82 will not be energized on detection offlame but rather by the operation of the timing circuit includingtransistor 70; contacts 60-7 open; and contacts 60-8 close. Thus anignition interval is initiated at the end of the first timing interval.

During the ignition interval, pilot fuel is orwing into the supervisedcombustion chamber and the ignition control is operative to initiateflame. Also, the timing interrvals controlled by the second and thirdtimers are running. With the application of power to the second timer, abias is applied to the output circuit of transistor 70 and the timingcapacitor 72 commences to charge. When that capacitor has sufficientcharge to overcome the bias, that Y transistor conducts and thecapacitor discharges through capacitor to pick up the relay. With thepickup of the flame relay, contacts -82-1 open, interrupting the circuitfor energizing the lockout actuator; contacts 82-2 close, providing analternate lockout actuator enabling circuit and also a circuit for theoutput circuit of timer transistor 1110; contacts 82-4 close, providinga holding circuit for the flame relay coil 82 if iiame is present in thecombustion chamber such that transistor 86 is in conducting condition;contacts 82-3 open, terminating operation of ignition control 26independently with the existence of ilame in combustion chamber; andcontacts 82-5 close in preparation for operation of the main fuelcontrol 28 upon the completion of the third timing interval. At thistime the ignition interval has terminated and pilot flame exists in thecombustion chamber.

The third timing circuit commenced operation coincidently with thesecond timing circuit, a bias being applied to transistor output circuit90 via biasing resistor 96 and the capacitor 92 commenced to charge.When the charge on capacitor 92 is sucient to overcome the bias ontransistor 90, that transistor conducts and capacitor 92 dischargesthrough relay coil 98 to pick up that relay. The closing of contacts98-2 completes a holding circuit via contacts 60-8 and resistor 126;contacts 98-1 open to interrupt one path to the lockout actuator;contacts 98-3 close to complete an alternate lockout actuator path inseries with the ame relay contacts #82-1 which are now open; andcontacts 98-4 close to operate the main fuel control 28 so that fuelflows into the main combustion chamber and is ignited from the pilot.llame. At this time both pilot and main flames are burning in thecombustion chamber.

Operation of the fourth timing circuit -was initiated with theenergization of the lllame relay coil 82 and capacitor 112 commenced tocharge. When the capacitor 112 charges sufficiently to overcome the biason transistor 110, that transistor conducts and that conductiontransition is applied by capacitor 112 to cause the output circuit oftransistor 120 to cease conducting so that coil 60 is de-energized. Withthat de-energization, contacts 60-1 reclose; contacts 60-2 open;contacts 60-3 open, de-energizing the inputs to the second and thirdtiming circuits; contacts 60-4 close, re-energizing the damper control22; contacts 60-5 open, de-energizing the pilot control 24; contacts60-6 close in a resetting operation, paralleling the now-closed llamerelay contacts 82-4; contacts 60-7 close, establishing a holding circuitfor coil 98; and contacts 60-8 open. (Coil 98 may have a copper slug orcapacitor connected to it to delay its dropout so that it is maintainedin picked up condition during this transition.)

Should flame failure occur at any time after detection of flame bysensor 62, transistor 86 will cease conducting and coil 82 will bede-energized causing all of its controlled contacts to return to theirnormal positions. Contacts 82-1 close, and, as contacts 98-3 are closed,current Iwill flo-w through the lockout actuator 44 causing theoperation of that lookout switch, opening lockout contacts 44-1 andde-energizing the primary transformer 32 and all the control circuitspromptly and closing contacts 44-2 to energize the alarm 18. Also,should air flow cease for any reason, all of the relays will bede-energized, terminating the ilow of fuel to the supervised combustionchamber and shutting down the system in safe condition.

Suitable values for the components are:

Resistor:

56, 76, 96 4709 54 1M 74, 94 150K 102 l-OK 114 2M 122, 126 3009 124 10K6 Capacitor: af. 52, 72 200 92 100 112 50 The arrangement of the circuitcomponents in this embodiment enables provision of the interrelatedtiming sequence with the four relays of compact configuration, the relay60 controlling four SPDT switches; the relay 82 having four poles, onepole being SPDT; the relay 98 having three poles, one pole being SPDT;and control relay 20 having two normally opened contacts. A wide rangeof timing values may be provided easily through adjustment of theadjustable resistors 54, 74 and 94 and 114. Each timed interval may beadjusted from times as short as two seconds to times up to one minuteand greater.

While a particular embodiment of the invention has been shown anddescribed, various modifications thereof will be apparent to thoseskilled in the art and therefore it is not intended that the inventionbe limited to the disclosed embodiment or to details thereof anddepartures may be made therefrom within the spirit and scope of theinvention as delined in the claims.

What is claimed is:

1. Burner control apparatus for use with a fuel burner installationhaving a combustion chamber, a fuel control for controlling the flow offuel to the combustion chamber and an ignition control for igniting fuelin the combustion chamber comprising:

a plurality of electronic timers, each said electronic timer beingindividually adjustable to vary the duration of its timing interval,

a rst of said timers being operative to initiate a timing interval forthe operation of said fuel control and a second of said timers beingoperative to terminate operation of said ignition control at the end ofits timing interval independently of the detection of ilame in thesupervised combustion chamber by a flame detector, the timing intervalsof said rst and second timers overlapping one another and providing acheck on the proper operation of the control apparatus.

2. The burner control apparatus as claimed in claim 1 and furtherincluding a third electronic timer, the timing interval of said thirdtimer being arranged so that at least one other timer is operatingconcurrently with said rst timer throughout the timing interval of saidfirst timer.

3. The 'burner control apparatus as claimed in claim 1 wherein each saidtimer includes a timing network including a capacitive timing element,the rate of charge of that capacitive element determining the timinginterval of said timer.

4. The control apparatus as claimed in claim 1 wherein each said timerincludes an active switch element and a load device, said switch elementbeing operative to energize said load device at the end of said timinginterval.

5. The control apparatus as claimed in claim 4 wherein said load deviceis a relay coil and further including a circuit including a normallyopen contact controlled by said relay coil connected in series with saidrelay coil for providing a holding circuit upon energization of saidrelay coil.

6. The burner control apparatus as claimed in claim 1 wherein saidinstallation further includes a blower control and further including athird electronic timer operative to initiate a timing interval at thesame time said blower control is actuated and to initiate operation ofsaid ignition control at the end of its timing interval.

7. Burner control apparatus for use with fuel burner installation havinga combustion chamber, a fuel control for controlling the flow of fuel tothe combustion chamber and an ignition control for igniting fuel in thecombustion chamber comprising:

a plurality of electronic timers, each said electronic of flame in saidcombustion chamber, circuitry folrlr'eiif timer being individuallyadjustable to vary the duration of its timing interval,

a rst of said electronic timers being responsive to initiation ofoperation of said ignition control to initiate a timing interval for theoperation of said fuel control; and

a second of said electronic timers being connected to terminateoperation of said ignition control at the end of its timing intervalindependently of the detection of ame in the combustion chamber,"

the timing intervals of said rst and second timers overlapping oneanother and providing a check on the proper operation of the controlapparatus.

8. The burner control apparatus as claimed in claim 7 wherein saidinstallation further includes a pilot fuel control and further includinga third electronic timer operative to terminate operation of said pilotfuel control, the timing interval of said third timer being arranged sothat at least one other timer is operating concurrently with said iirsttimer throughout the timing interval of said iirst timer. I

9. The burner control apparatus as clalmed 1n claim 8 wherein each saidtimer includes a timing network including a capacitive timing elementand an adjustable resistive timing element, the rate of charge of thatcapacitive element determining the timing interval ofv s'aid timer.

10. The control apparatus as claimed in claim `9 wherein each said timerincludes an active switch element and a load device, said switch elementbeing responsive to said timing element to energize said load device atthe end of said timing interval.

11. The Q control apparatus as claimed in claim 10 wherein said loaddevice is a relay coil and further including a circuit includingnormally open contact controlled by said relay coil connected in serieswith said relay coil for providing'a holding circuit upon energizationof said relay coil.

12. The burner control apparatus as claimed in claim 11 and furtherincludinga flame detector, a iame relay responsive. to signals from saidflame detector, said second electronic timer being operative to energizethe cgil of said'iiame relay a predetermined interval after initiationof an ignition interval independently of the existence iblower controlis actuated and to initiate operation of said 55` ignition control andsaid first electronic timer at the end of its timing interval.

14. In a combustion control system having an ignition control, a* mainfuel control, Aand a'ame detector, a

iiame, relaylreszponsive to signals from-'saidflame detector, 60ansle'ctronic timer responsive-toa request afoifaignit' n andoperative-to' energize .the coil of said"ame .relai predeterminedinterval afterinitiation of said ignition rev quest independently of theexistence of flame in a combustion chamber, circuitry for rendering saidflame relay responsive to said iiame detector prior to said'ignitioninterval, and a second circuit for maintaining said iiame relayenergized after said ignition interval only in response to detection ofiiame by said iiame detector.

15. In a combustion control system having an ignition control and a mainfuel control and a flame detector, a

llame relay responsive to signals from said iiame detector, y

a first electronic timer connected to initiate an ignition interval andto energize said iiame relay a predetermined time interval afterinitiation of said ignition interval i11- dependently of the existenceof flame in the combustion chamber and circuitry for maintaining saidllame relay energized only in response to the detection of ame by saidflame detector.

16. In a combustion control system having an ignition control and a mainfuel control and a flame detector, a flame relay responsive to signalsfrom said ame detector, said flame relay including a tapped coil, andsaid flame detector being connected to said coil to energize said flamerelay in response to detection of iiame by said flame detector, a firstelectronic timer including a unijunction transistor, a capacitor and avariable resistor arranged so that said transistor is switched toconducting condition in response to a predetermined charge on saidcapacitor, said transistor being connected to the tap of said coil toenergize said coil when said transistor is switched to conductingcondition, said iirst electronic timer being connected to initiate anignition interval andV to energize said flame relay a predetermined timeinterval after initiation of said ignition interval independently of theexistence of flame in the combustion chamber, and circuitry formaintaining said iiame relay energized only in response to the detectionof flame by said iiame detector.

17. Ihe circuitry as claimed in claim 16 and further including a controlrelay and a second electronic timer, said second electronic timer beingresponsive to said first electronic timer to initiate a timing intervaland being operative at the completion of said timing interval toyrelease said control relay.

18. The circuitry as claimed in claim 17 wherein said ame relay includesa tapped coil, said iirst and second electronic timers each include aunijunction transistor, a capacitor and a variable resistor arranged sothat said transistor is switched to conducting condition in response toa predetermined charge on said capacitor, said transistor of said iirsttimer being connected to the top of said coil to energize said coil whensaid transistor is switched to conducting condition and said flamedetector is connected to said coil to energize said flame relay inresponse 'to the'detection of iiame by said llame detector and saidsecondtimer operates a transistor switch to release said control relayupon completion of its timing interval.

References Cited UNITED STATES PATENTS 3,376,099 4/1968 Giuffrida et al.431-26 EDWARD G. FAVORS, Primary Examiner

